Method of finishing the surface of metal articles



Oct. 13, 1970 H. A. KALVONJIAN 3,533,921

METHOD OF FINISHING THE SURFACE 01" METAL ARTICLES Filed March 8, 1968United States Patent 3,533,921 METHOD OF FINISHING THE SURFACE OF METALARTICLES Harry A. Kalvonjian, Kenosha, Wis., assignor to Frost Co.,Kenosha, Wis., a corporation of Wisconsin Filed Mar. 8, 1968, Ser. No.711,793 Int. Cl. C23b /48; C231? 17/00 US. Cl. 20438 2 Claims ABSTRACTOF THE DISCLOSURE Production of smooth level electroplated metalcoatings on the irregular rough surface of a sand molded metal castingor other rough surfaced metal parts by first molding about the metalcasting a layer of plastic providing a smooth uniform base which is thenelectroplated.

This invention relates to the finishing of rough surfaced metal partssuch as metal forging orsand molded metal, and particularly brasscastings especially shaped ones such as plumbing traps for sinks whichare generally exposed and are chrome plated for esthetic appearance.

Hitherto such sand molded brass castings, which have rough irregularsurfaces, were electroplated with a succession of layers such as copper,nickel and finally chromium. However, before electroplating it wasnecessary to smooth and level out irregularities in the coating surfacesuch as by grinding, bufiing and finish polishing. At times there areleft some depressions which cannot be removed in this manner. At othertimes this grinding and bufling brings to light cavities which must bewelded to close them up.

In many instances portions of the casting became outof-round due togeneration of gases when the metal is poured about the core of theshape, i.e. trap being cast, and this also affects the external threadsat the opposed ends of the unit which are integrally cast or cut intothickened cast end portions. In all, some of such castings are sodefective that they must be entirely discarded. As a whole there wasabout 50% scrap in the prior process.

In accordance with the present invention, where I employ the castingsubstantially, as removed from the mold, with only minor tumbling toremove sand and flashings and subsequently mold thereover a plastic coatof smooth outer surface, the brass casting can be thinner than washeretofore necessary, while retaining required standard mold thickness,to the extent that one can save approximately one-third brass basestock. Further savings are in grinding, welding, and rejects.Out-of-round parts can be brought up to full roundness by means of theplastic layer, and the necessary external threads can be molded of thesame plastic at the time the plastic coating is molded about thecasting.

Thus, the advantages of the present invention are lighter weight oforiginal brass casting; elimination of costly surface preparation;elimination of the possibility of porosity showing up during polishingoperations; elimination of scrap during finishing operations because ofpoor surface conditions; production of a more uniform and imperviousWall on the end product; perfectly rounded outer contour of the finishedpieces; material increase in eye value; reduction in cost; and supplyingof the trade with a superior product at a reduction in cost.

The plastic molding can be conducted by employing a conventional screwinjection machine (not shown) which will deliver stock of substantiallyuniform temperature from beginning to end of the shot.

The plastic can be either ABS (acrylonitrile butadiene styrenecopolymer) or such plastics as polypropylene, polysulfone or otherhardenable resin. The plastic coating ice on the brass casting takes theform and polish of the plastic mold such that for example anout-of-round brass casting which has become wholly or partially so dueto generation of gases in molding can be produced in a piece ofperfectly round cross section and all voids and surface irregularitiesleveled off and smoothed out so as to provide a smooth base for thesubsequent metal plating without the former requirement of grinding,brushing and polishing.

The layer of plastic coating applied to the brass casting is generallyfrom .030 to about .050 inch in thickness, being adequate to completelycoat the rough outside surface of the brass casting and correct anyout-of-round that may be found therein, thus eliminating surfacefinishing prior to plating.

The plastic coating is plated with a chrome finish in known manner suchas by first subjecting the part to conventional treatment such ascleaning, acid treatment, sensitization by immersion in a solution oftin, titanium, or other readily oxidized metallic salt. Adsorption ofthe sensitized material on the surfaces of the plastic prepares it forthe activating procedure. In the activating step, the plastic surface ismade catalytic so that a firm adherent metal coating will be depositedin the subsequent electrodeless plating step. The catalysts for thispurpose are generally precious metals such as gold, silver and paladium,this step of catalyst application being generally called seeding ortreating the plastic surface with a solution containing a salt of thecatalytic material. Oxidation of the tin or other sensitizer reduces thecatalytic precious metal salt to neuclei of the corresponding metalwhich nuclei clings to the surface of the plastic. Thereafter, thecatalyst plastic surface is immersed in an electrodeless copper ornickel plating bath, the catalytic action of the precious metal nucleireducing the plating metal out of solution so that it deposits on theplastic surface. This electrodeless plating step provides the plasticwith a surface that can then be electroplated by standard procedures ofthe electroplating industry and in this case desirably with added nickelplating and a final chrome plating.

Other objects and advantages of the present invention relate to detailsof construction, arrangement of parts and the economies thereof as willbe apparent from a consideration of the following specification andaccompanying drawings wherein:

FIG. 1 diagrammatically illustrates a mold and a sink trap disposedtherein and with a plastic layer molded thereabout.

FIG. 2 is a perspective view of a sink trap formed in accordance withthe present invention.

FIG. 3 is a section on the line 3-3 of FIG. 2.

FIG. 4 is a section on the line 44 of FIG. 2.

Referring to the drawings, the reference numeral 10 indicates a moldhalf wherein a sink trap 11 which was previously cast in a sand mold inconventional manner is disposed and retained in position by means of thecircular plug-like mold portions 12 and 13 which extend into the opposedends of the trap and by means of the plug member 14 which extends intothe drain opening 15 of the trap. The members 12, 13 and 14 serve toclose up the openings of the brass casting and in addition position itwithin the cavity of the mold so that even though the brass casting mayoriginally be out of round as shown in FIG. 3, the layer of plastic 16molded thereabout, as also shown in FIG. 3, will be round and compensatefor the out-of-roundness of the brass casting 11. It will be noted thatthe plastic layer 16 is molded with integral threads wherever necessarysuch as 17 and 18. The cavity of the mold 10 is smooth so as to providethe injection mold layer 16 with a smooth outer contour. Afterpreparation thereof as previously described it is electroplated with oneor more layers of metal, jointly indicated as 19,

in the previously described manner which is now conventional for theelectroplating of plastics.

Although for the purpose of illustration I have shown a brass sink trap,castings of other metals and of other shapes are amenable to the processof the present invention as will be readily understood by those skilledin the art.

Iclaim:

1. The method of finishing the surface of a metal product, whichcomprises molding a plastic coating in a die completely about and tosaid metal product to form a continuous plastic coating, integrallymolding threads in the plastic coating, and then electroplating with atleast one layer of bright metal.

2. An article comprising a rough irregular surfaced metal product, anouter surface layer of plastic molded completely about and bonded tosaid metal product, ex-

ternal threads molded in said plastic, and electroplated metal coveringand bonded to said plastic layer.

References Cited UNITED STATES PATENTS HOWARD S. WILLIAMS, PrimaryExaminer R. L. ANDREWS, Assistant Exxaminer U.S. Cl. X.R.

